Volvo 940 Turbo problem

Update to a previous question.

My turbo unit is working but I am not getting the speed I used to out of the car.

When the turbo is engaged I can hear a intermitent whooshing sound.

Following on from previous advice I fitted a new induction pipe leading from the air mass meter to the turbo.

Tried it out tonight and I can still only get about 75mph

Is there anything else I am missing.

I do not think it is a clogged catalytic converter as there is no smoke from the exhaust. All other pipe look OK.

Please can someone help as this is annoying me now